Interpretive Summary: Refrigerated cucumber pickle products are typically not heat processed, and are acidified with a relative amount of acetic acid compared to room temperature, shelf stable pickles. For these products, refrigeration helps to inhibit the growth of spoilage bacteria and maintain flavor, texture and appearance of the pickles, however, we found that some disease causing bacteria can survive for extended periods in brines typical of refrigerated pickles. To address this problem we developed methods to assure the disease causing bacteria were killed. We found that addition of fumaric acid to a refrigerated pickle brine formulation accelerated the die-off of E. coli compared to a typical brine formulation. Fumaric acid is a intermediate in the normal energy metabolism of plants and animals and a generally regarded as safe (GRAS) food acidulant. The results demonstrate that modified brine solution with fumaric acid enhanced the safety of acidified pickle products without significantly altering the acceptability of refrigerated dill pickles. This gives manufacturers a way to improve the safety of the product without altering its characteristics.

Technical Abstract:
Refrigerated cucumber pickle products cannot be heat processed due to the loss of characteristic sensory attributes. Typically brined refrigerated pickles contain less than 100 mM acetic acid with pH values of 3.7 to 4.0. Refrigeration (4 to 10 ºC) helps to inhibit the growth of spoilage bacteria and maintain flavor, texture, and appearance of the pickles. Previous research has shown that pathogenic Escherichia coli strains are unusually acid resistant and survive better in refrigerated acid solutions than at higher temperatures. We found that E. coli O157:H7 can survive for 1 mo or longer at 4 ºC in brines typical of commercial refrigerated pickles. Our objective was to develop methods to assure a 5-log reduction of pathogenic E. coli in these types of products, while maintaining the sensory characteristics. A novel brine formulation was developed, based on current commercial refrigerated pickle brines, which contained 25 mM fumaric acid, 5 mM benzoic acid, 70 mM acetic acid, and 342 mM (2%) sodium chloride, with a pH of 3.8. Sensory data indicate that this formulation did not affect flavor or other sensory attributes of the product, compared to traditional formulations. We achieved a 5-log reduction of E. coli O157:H7 at 30 ºC for 1.52 ± 0.15 d, at 20 ºC for 3.12 ± 0.34 d, or at 10 ºC for 8.83 ± 0.56 d. Growth of lactic acid bacteria was also inhibited. These results can be used by manufacturers to assure a 5-log reduction in cell numbers of E. coli O157:H7 and Salmonella without a heat process during the manufacture of refrigerated pickle products.